Photoionization of Ca in a static electric field

Abstract

We present a joint theoretical and experimental investigation for electric-field effects on ground-state photoionization of Ca. For an electric field with its direction along the z axis, the dominant field-free, doubly excited, odd-parity (i.e., 3dnp and/or 3dnf ) resonances of the 1,3 L o J =1 (i.e., 1,3 P o J =1 and 3 D o J =1 ) symmetries are coupled with the even-parity (i.e., 3dns, 3dnd, and/or 3dng) resonances of the 1,3 L e J =0 (i.e., 1 S e J =0 and 3 P e J =0 ) and 1,3 L e J =2 (i.e., 3 P e J =2 , 1,3 D e J =2 , and 3 F e J =2 ) symmetries. Using a B-spline-based complex-rotation method with spin-dependent interaction, our theoretically calculated spectrum is found to be in good agreement with the observed spectrum from a cross-beam photoionization experiment for field strengths up to 25 kV/cm. We present in detail a number of qualitative features of the field-induced level crossing and avoided crossing in energy between neighboring resonances, their corresponding changes in width, and the resulting variation in resonance structure profiles. A few "hidden" resonances due to strong overlap with more prominant resonances are also identified theoretically. PACS number(s): 32.80. Fb, 32.80.Zb, 32.70.Jz, 31.15.vj J =1 (i.e., 1,3 P o J =1 and 3 D o J =1 ) symmetries and the even-parity resonances of 1,3 L e J =0 (i.e., 1 S e J =0 and 3 P e J =0 ) and 1,3 L e J =2 (i.e., 3 P e J =2 , 1,3 D e J =2 , and 3 F e J =2 ) symmetries. We focus our discussion on the crossing and avoided crossing in energy between overlapping resonances, their corresponding changes in resonance widths, and the variation in resonance 1050-2947/2010/82(6)/063402 (12) 063402-1 J =2 ) symmetries by the external electric feld for the M J = 0 components. The photoionization cross section σ (E) from the initial ground state